Reciprocating air motors of the type which are used to drive reciprocating fluid pumps have been in use for many years. One of the drawbacks to such air motors is their tendency to ice up when operated continuously due to the repeated condensation of moisture and associated cooling which takes place during operation, particularly in the air valve mechanism.
U.S. Pat. No. 4,921,408 (commonly assigned with the instant invention and hereby incorporated by reference) deals with one aspect of decreasing icing during operation, and the instant invention deals with another aspect.